The present invention relates to a process and an apparatus for building a green tire in a process for producing a radial tire.
Conventional methods have been developed for building a green tire.
Firstly, a tire carcass is wound on a tire shaping former including right and left shoulder formers, and formed into a cylindrical shape. Then, beads are set in specified positions on the tire carcass. In this state, bead locking mechanism provided in the respective shoulder formers are expanded in a radial direction of the shaping former, whereby the beads are locked in the tire carcass. Subsequently, while the shaping air is supplied to inflate the tire carcass, the left and the right shoulder formers are moved closer to each other by a driving mechanism, narrowing the distance between the beads. In this way, the tire carcass is shaped into a toroidal form. Thereafter, opposite side portions of the tire carcass are turned up around the respective beads. Consequently, a breaker and a tread are further applied onto an outer circumferential surface of the tire carcass, whereby a green tire is completely built.
For carrying out the above process, an apparatus is used having a main shaft supported by a housing rotatably and movably in an axial direction thereof, and a countershaft (sleeve) externally fitted to the main shaft and being rotatable together with the main shaft and movable in an axial direction thereof relative to the main shaft. The apparatus also includes left and right shoulder formers fixed to forward ends of the main shaft and the countershaft, each shoulder former being provided with radially expandable bead locking mechanism and inflatable ply turn-up device. A pair of ladder-shaped screw shafts, angular screw shafts, or ball screws, each having a left-handed screw portion and a right-handed screw portion, are rotatably supported by the shoulder formers in parallel to the main shaft. A member provided with holes having internal right-hand screw threads on opposite sides thereof are connected to the screw shafts and the countershaft in the following fashion. The holes of the member are spirally fitted to the right-hand screw portions of the respective screw shafts. A center portion of the member is so connected to a rearward end of the countershaft as to render the countershaft rotatable and slidable. In addition, a member provided with holes having internal left-hand screw threads on opposite sides thereof is connected to the screw shafts and the main shaft in the following fashion. The holes of the member are spirally fitted to the left-hand screw portions of the respective screw shafts. A center portion of the member is so connected to a rearward end of the main shaft as to render the main shaft rotatable and slidable. The screw shafts are coupled to a motor. By reciprocatingly rotating the screw shafts by the motor, the main shaft and the countershaft can be moved in the axial direction thereof relative to each other. Accordingly, the shoulder formers fixed respectively to the main shaft and the countershaft can be moved closer to or away from each other. In other words, in this apparatus, the driving force of a drive source, such as a motor, is transmitted respectively to the main shaft and the countershaft through a desired driving force transmission mechanism, whereby the main shaft and the countershaft are moved closer to and away from each other.
However, in the above process and apparatus, the left and the right shoulder formers are coupled to the driving mechanism through the main shaft or the countershaft respectively. Unless driven by the driving mechanism, the shoulder formers are in almost completely fixed states respectively. Accordingly, the following problems occur.
FIG. 7(a) shows the state of an over hanging carcass ply C mounted on a turn-up bladder (ply turning up bladder) 63. In this state, left and right shoulder formers on which the carcass ply C is wound (only one of the shoulder formers 70 is shown in FIG. 7(a)) are fixed, and therefore the distance between the two shoulder formers is unchangeable.
FIG. 7(b) illustrates the state of the device when bead locking segment 64a (Serving as a bead locking mechanism) is radially expanded. As the carcass ply C is pushed radially outward, a portion of the carcass ply C is lifted from a point P serving as a starting point. Accordingly, cords of the carcass ply C are elongated a distance obtained by subtracting a length (L1+l1) as shown in FIG. 7(a) from another length (L2+l2 as shown in FIG. 7(b). Such elongation of the cords can be compensated by displacement of an end of the ply from a position E to a position E'. Alternatively, the elongation of the cords can be compensated by displacement of a point P' shown in FIG. 7(b) to the point P. These two types of cord displacement occur at different ratios. This causes variation in the lengths of the carcass ply cords between the beads adversely affecting uniformity of the tire.
Further, displacing the end of the ply from the position E to the position E' cause the cord angle constituting a bead reinforcing layer with respect to its lengthwise direction to increase. This in turn causes the angles of the carcass ply cords with respect to a circumferential direction of the carcass ply to become greater, again adversely affecting the tire uniformity. Moreover, displacing the end of the ply from the position E to the position E' causes great tension be exerted onto the carcass ply cords thereby reducing the amount Tat topping rubber of a portion U of the carcass ply C immediately adjacent the bead B. In this state, the bead and the ply cords are liable to be abraded one against another.
Furthermore, in the above process and apparatus, when the left and the right shoulder formers are driven for moving them closer to each other in the carcass shaping operation, it is extremely difficult to start driving the left and the right shoulder formers in perfect synchronization with the start of the supply of the shaping air. If the shoulder formers are driven after the start of the supply of the shaping air, the carcass ply C is pulled excessively by the shaping air causing the bead on the carcass ply C to dislocate from set positions thereof. Accordingly, there is a greater likelihood that the lengths of the turned up ply and the distance between the beads will vary. On the contrary, if the shoulder formers are driven before the start of the supply of the shaping air, problems such as flapping of the carcass ply occur during the carcass shaping operation.